In this section, we'll implement a compass using the LEDs on the micro:bit. Like proper compasses, our LED compass must point north somehow. It will do that by turning on one of its outer LEDs; the LED turned on should point towards north.
Magnetic fields have both a magnitude, measured in Gauss or Teslas, and a direction. The magnetometer on the micro:bit measures both the magnitude and the direction of an external magnetic field but it reports back the decomposition of said field along its axes.
The magnetometer has three axes associated to it. The X and Y axes basically span the plane that is the floor. The Z axis is pointing "out" of the floor, so upwards.
You should already be able to write a program that continuously prints the magnetometer data on the RTT console from the I2C chapter. After you wrote that program, locate where north is at your current location. Then line up your micro:bit with that direction and observe how the sensor's measurements look.
Now rotate the board 90 degrees while keeping it parallel to the ground. What X, Y and Z values do you see this time? Then rotate it 90 degrees again. What values do you see?